1. Field of the Invention
The invention relates to a device for converting rotary motion into axial motion wherein an electric motor rotates a plurality of rollers to drive a thrust element in an axial direction.
2. Description of the Prior Art
A device for converting rotary motion into axial motion is known in the prior art. For example German Utility Model 8702 656.2 discloses a device for converting rotary motion into axial motion.
In addition, U.S. Pat. No. 5,121,019 to Pradler, now expired, discloses a linear drive unit comprising an electric motor, a three-stage planetary step down gear means, a conversion drive, and a driven rod disposed within a housing. In particular, the conversion drive in Pradler suffers from the disadvantage in that the design of FIG. 3a shows a double engagement for revolving members 166. This is because threads 172 on revolving members 166 simultaneously engage thread 160 of central part 150 and thread 164 of driven rod 64. Furthermore, this engagement occurs along the same axial position in rolling members 166 leaving little tolerance for threads 172 to move while engaging drive body 92 and driven rod 64.
The present invention is designed as an improvement over the prior art because this invention is designed to avoid the double engagement of the drive grooves on the planetary rollers between the drive shaft and the axially driven thrust element.